This project seeks to develop an earphone for diagnostic audiometry with features that will significantly increase the efficiency and decrease the cost of routine hearing testing. The most-often used earphones emply a supra-aural design that has several undesirable characteristics, including 1) an "occlusion effect", an artificial increase in sensitivity to bone-conducted stimuli; 2) poor ambient noise exclusion; 3) excessive transcranial conduction of sound; 4) high inter-subject variability in sound pressures delivered to human ears; and 5) poor comfort. The occlusion effect necessitates that the test ear be uncovered during bone conduction testing. This requires that the tester change the transducer arrangement several times during pure tone testing. In manual testing, this requirement can add several minutes to the test time. For automated testing, the need to reposition transducers several times during the test is unacceptable because it is counterproductive to the goal of reducing personnel costs., The poor ambient noise exclusion requires that testing be performed in expensive sound rooms. The excessive transcranial conduction of sound results in errors associated with responses by the non-test ear that cannot always be eliminated by masking noise. The inter-subject variability results increases the variance associated with threshold measures. The poor comfort limits the time that some patients will participate in the test. Other earphones are available that address some, but not all, of these problems. In this project, an earphone will be developed that 1) minimizes the occlusion effect permitting the entire pure tone hearing test to be conducted with a single transducer arrangement and facilitating automated test methods; 2) increases ambient noise exclusion, eliminating (in many environments) the need for sound-attenuating rooms; 3) decreases transcranial conduction of sound resulting in fewer errors associated with responses of the non-test ear; 4) decreases inter-subject variability; and 5) increases comfort. In addition to meeting these goals, the earphone must have a frequency response that is similar to other audiometric earphones to avoid significant changes in the frequency content of stimuli used for speech tests.